1. Field of the Invention
This invention relates to rigid polyurethane foams and a method for manufacturing the same.
2. Description of the Prior Art
Rigid polyurethane foam is fabricated from
organic polyisocyanate; PA1 organic polyol; PA1 halogenated alkane blowing agents; PA1 surfactants; PA1 catalysts for the reaction of --OH and --NCO radicals. PA1 organic polyisocyanate; PA1 organic polyol; PA1 halogenated alkane blowing agent; PA1 surfactant; PA1 catalyst for the reaction of --OH and --NCO radicals. PA1 an organic polyisocyanate--which can be a monomeric polyisocyanate, a polymeric polyisocyanate or a polyisocyanate prepolymer; PA1 an organic polyol which may be a polyether, a polyester, a mixed polyether-polyester, or a mixture of polyethers and polyesters; PA1 a halogenated alkane blowing agent such as trichlorofluoro methane; PA1 a surfactant, usually an alkoxylated silicone; PA1 a catalyst for the reaction of --OH and --NCO
Rigid polyurethane foam can be produced by combining the listed ingredients in a free-rise environment or by combining the listed ingredients in a closed mold. When manufactured in a free-rise environment, rigid polyurethane foam is customarily employed as a filler material wherein its compressive strength and shear strength are not usually significant factors. Because the resulting rigid polyurethane foam is intended to be used as a filler, the lowest feasible densities are usually desirable for free-rise foam.
When rigid polyurethane foam is employed in a closed mold, there is a tendency for the material to have a greater density at the skin of the mold than at the interior. The resulting molded foam article has a differential density; the core has a density which may be substantially lower than the skin density.
Where polyurethane foam products are intended for fire retardant applications, it is customary to employ halogenated organic polyols, at least in part, as a component of the organic polyol ingredients. The resulting rigid polyurethane foam is evaluated by ASTM E84 to determine its flame spread and smoke generation properties.
Rigid polyurethane foam products have included a variety of organic polyol ingredients including polyethers, polyesters and mixtures thereof.
The use of a polyalkylene terephthalate digestion product in flexible polyurethane foam is described in U.S. Pat. No. 4,048,104. Therein, the digestion product and its preparation are described. However in that instance the digestion product is employed to prepare polyisocyanate prepolymers--and not as a polyol ingredient in the fabrication of flexible polyurethane foam.